A conventional phased antenna array is made up of multiple antenna elements that are connected to a common source through an RF power divider/combiner network. The relative amplitude and phases of the different signals feeding the antennas are varied such that the effective radiation pattern of the array is reinforced in a particular direction. These phased arrays work both in transmit and receive modes to communicate the modulated active signals. In contrast, RFID readers that use multiple antennas use a passive backscatter modulation technique where a reader antenna radiates an RF signal that illuminates RFID tags, and the tags modulate the impinging RF energy and re-radiate a passive modulated signal back to the reader.
Conventional passive UHF RFID (ultra high frequency radio-frequency identification) systems use an RFID reader that generates RF signals to query RFID tags within an RF zone near the reader. The RF zone cannot be exactly defined within the practical limits of business environments. For example, tags near the edge or outside of an RF reader zone may inadvertently be read and associated with tags located inside the zone. Consequently, human intervention is needed to distinguish between tags inside and outside of the RF zone. Unintended association of tags could occur with tags in adjacent portals, with tags on a forklift and adjacent to a forklift, and with tags adjacent to racks of apparel.
Automatic techniques implemented in “middle-ware” business logic, such as measuring the time or number of occurrences that a tag was read, help to distinguish between tags and mitigate the number of exceptions. Statistical techniques that use the time, number, or strength of the tags' signals help to reduce the number of unintended associations, but statistics inherently have exceptions that will require exception processing with human intervention. Such statistical techniques are not based on the location of a tag.
There is a need for a system that overcomes the above problems, as well as providing additional benefits. Overall, the above examples of some related systems and associated limitations are intended to be illustrative and not exclusive. Other limitations of existing or prior systems will become apparent to those of skill in the art upon reading the following Detailed Description.